Semiconductor device and a method of manufacture therefor

ABSTRACT

The present invention provides a semiconductor device, a method of manufacture therefor, and an integrated circuit including the aforementioned semiconductor device. The semiconductor device, in accordance with the principles of the present invention, may include a substrate, and a graded capping layer located over the substrate, wherein the graded capping layer includes at least two different layers, wherein first and second layers of the at least two different layers have different stress values.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to a semiconductordevice, more specifically, to a semiconductor device having a gradedcapping layer and a method of manufacture therefor.

BACKGROUND OF THE INVENTION

To accommodate higher packing density in present integrated circuits,electrical connections to integrated circuit devices formed in asemiconductor substrate are made by multilayer interconnects. Each levelof multilayer interconnects is supported over the semiconductorsubstrate by an interlevel dielectric. Generally, the integrated circuitstructure includes a dielectric layer and metal lines are laid down inparallel strips on top of the dielectric layer. Additional levels ofmultilayer interconnects are formed over this dielectric layer, eachincluding additional metal interconnects and an interlevel dielectriclayer.

Fluoro-silicate glass (FSG) is one such material used as an inter-metaldielectric in semiconductor backend processing. FSG is used for manyreasons, however, it is particularly well suited as a result of itsimproved gapfill capacity and reduced oxide dielectric constant.Lowering the dielectric constant reduces the inter/intra levelcapacitance of the metal lines, enhancing the operating speed of thedevices.

FSG is often capped with a silicon-rich oxide (SRO) layer. The SRO layerattempts to reduce, if not prevent, fluorine from diffusing from the FSGlayer to the bottom Ti/TiN metal stack. The SRO is typically depositedusing a plasma enhanced chemical vapor deposition (PECVD) process.Often, however, this PECVD process causes the SRO layer to have variousdegrees of stress, depending on the deposition conditions. Therefore,the stress of the SRO layer can be tailored to go from slightly tensile,to highly compressive, depending on these conditions.

The most prevalent deposition condition that controls this degree ofstress is the frequency at which the SRO layer is deposited. Forexample, the SRO layer may be deposited using a single or dual frequencyprocess. As compared to a single frequency process, a dual frequencyprocess requires that both the upper and lower electrodes be modulatedat a particular, and often different, frequency.

The conventional practice is to deposit a single layer of slightlytensile SRO on top of the FSG layer using the single frequency process.Unfortunately, the tensile stress of the aluminum dominates the totalstress, and the wafer becomes increasingly warped as themetal/dielectric levels are formed. A way to minimize this wafer warpageis to deposit a highly compressive SRO layer to counteract the tensilestress of the aluminum layer. This highly compressive SRO layer istypically formed using the aforementioned dual frequency process.Nevertheless, the highly compressive SRO layer often causes excessivelateral diffusion of fluorine to occur, which may further lead to metalattack.

Accordingly, what is needed in the art is a capping layer, or method ofmanufacture therefore, that does not introduce the problems introducedby the prior art capping layers.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides a semiconductor device, a method ofmanufacture therefor, and an integrated circuit including theaforementioned semiconductor device. The semiconductor device, inaccordance with the principles of the present invention, may include asubstrate and a graded capping layer located over the substrate, whereinthe graded capping layer includes at least two different layers, whereinfirst and second layers of the at least two different layers havedifferent stress values.

As previously mentioned, the present invention also provides a methodfor manufacturing the semiconductor device disclosed above. Among othersteps, the method includes providing a substrate, and forming a gradedcapping layer over the substrate. In this embodiment the graded cappinglayer includes at least two different layers, wherein first and secondlayers of the at least two different layers have different stressvalues.

Additionally, the present invention provides an integrated circuitincluding the aforementioned semiconductor device. The integratedcircuit, among other elements, includes: (1) transistors located over asemiconductor substrate, (2) an interlevel dielectric layer located overthe transistors, (3) a graded capping layer located over the interleveldielectric layer, wherein the graded capping layer includes at least twodifferent layers, wherein first and second layers of the at least twodifferent layers have different stress values, and (4) interconnectslocated in the interlevel dielectric layer for contacting thetransistors and thereby forming an operational integrated circuit.

The foregoing has outlined preferred and alternative features of thepresent invention so that those skilled in the art may better understandthe detailed description of the invention that follows. Additionalfeatures of the invention will be described hereinafter that form thesubject of the claims of the invention. Those skilled in the art shouldappreciate that they can readily use the disclosed conception andspecific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read with the accompanying FIGUREs. It is emphasized that inaccordance with the standard practice in the semiconductor industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion. Reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of one embodiment of asemiconductor device constructed according to the principles of thepresent invention;

FIG. 2 illustrates a cross-sectional view of a partially completedsemiconductor device at an initial stage of manufacture;

FIG. 3 illustrates a cross-sectional view of the partially completedsemiconductor device illustrated in FIG. 2 after formation of asubstrate over the conductive features;

FIG. 4 illustrates a cross-sectional view of the partially completedsemiconductor device illustrated in FIG. 3 after beginning to form agraded capping layer, for example by forming a first layer;

FIG. 5 illustrates a cross-sectional view of the partially completedsemiconductor device illustrated in FIG. 4 after continuing to form thegraded capping layer, for example forming a second layer; and

FIG. 6 illustrates a cross-sectional view of an integrated circuit (IC)incorporating a graded capping layer constructed according to theprinciples of the present invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is a cross-sectional view ofone embodiment of a semiconductor device 100 constructed according tothe principles of the present invention. In the embodiment illustratedin FIG. 1, the semiconductor device 100 includes a substrate 110 havingconductive features 120 located thereon. The substrate 110 might be aninterlevel dielectric layer and the conductive features 120 might berunners located on the dielectric layer 110 for connecting variousfeatures in the semiconductor device 100. Other dielectric layers andconductive features are within the scope of the present invention.

Located over the dielectric layer 110 and the conductive feature 120 isa substrate 130. The substrate 130, similar to the substrate 110, maycomprise an interlevel dielectric layer. In the particular embodimentshown and discussed with respect to FIG. 1 the substrate 130 is aninterlevel dielectric layer comprising fluoro-silicate glass (FSG).Nevertheless, the substrate 130 may comprise other layers and staywithin the scope of the present invention.

Positioned over the substrate 130 is a graded capping layer 140. Thegraded capping layer 140 is typically designed to reduce the amount ofdopant diffusion within the semiconductor device 100. In the particularembodiment of FIG. 1, the graded capping layer 140 comprises asilicon-rich oxide, and is designed to reduce, or substantially prevent,fluorine diffusion from the FSG substrate 130 to other areas of thesemiconductor device 100.

The graded capping layer 140, in accordance with the principles of thepresent invention, includes at least two different layers. In theembodiment of FIG. 1, the graded capping layer 140 includes a firstlayer 143 and a second layer 148, wherein the first and second layers143, 148, have different stress values from one another. Particularly,the first and second layers 143, 148, have different compressive stressvalues from one another. While the graded capping layer 140 isillustrated in FIG. 1 as including only the first and second layers 143,148, those skilled in the art understand that the present invention isnot limited by this, and that any number of layers, particularly fromabout 2 to about 6 layers, might be used. Similarly, the graded cappinglayer 140 may have a range of thicknesses, including a thickness rangingfrom about 200 nm to about 600 nm.

In an exemplary embodiment, whether the graded capping layer 140includes only the first and second layers 143, 148, or an infinitenumber of layers, the stress value of the layers increases as theindividual layers move away from the substrate 130. In particular, eachof the individual layers desirably has a compressive stress valueranging from about 10 MPa to about 100 MPa. For example in theembodiment of FIG. 1, the first layer 143 of the graded capping layer140 optimally has a compressive stress value ranging from about 30 MPato about 40 MPa and the second layer 148 has a compressive stress valueranging from about 70 MPa to about 90 MPa.

Unique to the present invention is the ability to use the graded cappinglayer 140 to reduce dopant diffusion without imparting the stress issuesintroduced by the prior art. For example, the graded capping layer 140of the present invention does not introduce the wafer warpage introducedwith using a single layer tensile stressed capping layer. Additionally,the graded capping layer 140 of the present invention does notexperience the lateral dopant diffusion experienced by the single layercompressive stressed capping layer. Accordingly, the graded cappinglayer 140 allows the present invention to compensate for the hightensile stress in the aluminum without accelerating the lateral dopantdiffusion.

Turning now to FIGS. 2-5, illustrated are cross-sectional views ofdetailed manufacturing steps instructing how one might, in anadvantageous embodiment, manufacture an semiconductor device similar tothe semiconductor device 100 depicted in FIG. 1. FIG. 2 illustrates across-sectional view of a partially completed semiconductor device 200at an initial stage of manufacture. The partially completedsemiconductor device 200 includes a substrate 210 having conductivefeatures 220 located thereon. As previously recited, the substrate 210could be an interlevel dielectric layer or another similar layer, aswell as the conductive features 220 could be interconnects, runners,etc. Both the substrate 210 and conductive features 220 have beenconventionally formed.

Turning now to FIG. 3, illustrated is a cross-sectional view of thepartially completed semiconductor device 200 illustrated in FIG. 2 afterformation of a substrate 310 over the conductive features 220. Moreoften than not, the substrate 310 is an interlevel dielectric layer, inwhich case it might have a thickness ranging from about 1.0 μm to about2.0 μm, and more particularly a thickness of about 1.6 μm.

The substrate 310 may comprise a number of different materials whilestaying within the scope of the present invention. In the particularembodiment shown in FIG. 3, however, the substrate 310 comprisesfluoro-silicate glass. In the instance the substrate 310 is afluoro-silicate glass interlevel dielectric layer, the substrate 310might be formed using a plasma enhanced chemical vapor deposition(PECVD) process employing a mixture of SiH₄, SiF₄, O₂ and Ar gases.Additionally, the substrate 310 could be formed employing a depositiontemperature ranging from about 300° C. to about 500° C., with an optimaltemperature of about 400° C. As control of the fluorine content in thesubstrate 310 may be important, other deposition conditions, such as gasflows, pressure, top power/side power, bias power, etc., may beoptimized to provide the specific desired fluorine content. Whilecertain specifics have been given with respect to forming the substrate310, those skilled in the art understand that a number of differentprocesses and conditions might be used to form the substrate 310.

Turning now to FIG. 4, illustrated is a cross-sectional view of thepartially completed semiconductor device 200 illustrated in FIG. 3 afterbeginning to form a graded capping layer 410, for example by forming afirst layer 420. The first layer 420, which may have a thickness rangingfrom about 100 nm to about 300 nm, and particularly a thickness ofaround about 200 nm, comprises a silicon-rich oxide in the embodimentillustrated in FIG. 4. Other types of material and thicknesses are,however, within the scope of the present invention.

The first layer 420 may be formed using a dual frequency PECVD process.As those skilled in the art are well aware, a dual frequency PECVDprocess requires that both the upper and lower electrodes be modulatedat a particular, and often different, frequency. This dual frequencyprocess, which may be conducted at an RF power ranging from about 500Watts to about 700 Watts, depending on the electrode, provides theprecise compressive stress desired in the first layer 420. For example,the precise compressive stress desired in the first layer 420, amongothers, should range from about 30 MPa to about 40 MPa. Similarly, thefirst layer 420 may be formed using a mixture of SiH₄, N₂0 and N₂ at adeposition temperature ranging from about 300° C. to about 500° C., withan optimal temperature of about 400° C.

Turning now to FIG. 5, illustrated is a cross-sectional view of thepartially completed semiconductor device 200 illustrated in FIG. 4 aftercontinuing to form the graded capping layer 410, for example by forminga second layer 510. Similar to the first layer 420, the second layer 510may have a thickness ranging from about 100 nm to about 300 nm, andparticularly a thickness around about 200 nm. Additionally, the secondlayer 510 may comprise a silicon-rich oxide as depicted in theembodiment illustrated in FIG. 5. Other types of material andthicknesses are, however, within the scope of the present invention.

Similar to the first layer 420, the second layer 510 may be formed usinga dual frequency PECVD process. This dual frequency process, which maybe conducted at an RF power ranging from about 500 Watts to about 700Watts, depending on the electrode, provides the precise compressivestress desired in the second layer 510. For example, the precisecompressive stress desired in the second layer 510, among others, shouldrange from about 70 MPa to about 90 MPa. Similarly, the second layer 510may also be formed using a mixture of SiH₄, N₂0 and N₂ at a depositiontemperature ranging from about 300° C. to about 500° C., with an optimaltemperature of about 400° C.

After completing the partially completed semiconductor device 200illustrated in FIG. 5, additional layers of the graded capping layercould be formed over the second layer 510, or alternatively themanufacturing process could halt, resulting with a completedsemiconductor device similar to the semiconductor device 100 illustratedin FIG. 1. If additional layers were to be formed, many of thespecifications of the first and second layers 420, 510, described abovemight change. Particularly, the compressive stress values for the firstand second layers 420, 510, might change to accommodate the additionallayers. Regardless of the situation, the graded capping layerconstructed in accordance with the principles of the present inventiondoes not experience and/or introduce the issues experienced and/orintroduced by the prior art capping layers. Particularly, the gradedcapping layer does not impart the wafer warping introduced by theconventional single layer tensile capping layer. Additionally, thegraded capping layer does not allow the substantial dopant diffusionallowed by the conventional single layer compressive capping layer.

Referring finally to FIG. 6, illustrated is a cross-sectional view of anintegrated circuit (IC) 600 incorporating a graded capping layerconstructed according to the principles of the present invention. The IC600 may include devices, such as transistors used to form CMOS devices,BiCMOS devices, Bipolar devices, or other types of devices. The IC 600may further include passive devices, such as inductors or resistors, orit may also include optical devices or optoelectronic devices. Thoseskilled in the art are familiar with these various types of devices andtheir manufacture.

In the particular embodiment illustrated in FIG. 6, the IC 600 includessemiconductor devices 610 located between isolation structures 620. TheIC 600 of FIG. 6 further includes dielectric layers 630 located over thesemiconductor devices 610. In accordance with the principles of thepresent invention, a graded capping layer 640 is located over thedielectric layers 630. Additionally, contacts 650 are located within thedielectric layers 630 to interconnect various devices, thus, forming theoperational IC 600.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. A semiconductor device, comprising: a substrate; and a graded capping layer located over said substrate, wherein said graded capping layer includes at least two different layers comprising the same material, wherein first and second layers of said at least two different layers have different stress values.
 2. The semiconductor device as recited in claim 1 wherein said substrate comprises an interlevel dielectric material.
 3. The semiconductor device as recited in claim 2 wherein said interlevel dielectric material comprises fluoro-silicate glass.
 4. The semiconductor device as recited in claim 1 wherein said graded capping layer includes from about 2 to about 6 different layers, each of said different layers having different stress values.
 5. The semiconductor device as recited in claim 1 wherein said first and second layers have different compressive stress values.
 6. The semiconductor device as recited in claim 5 wherein said compressive stress values of said first and second layers increase as said layers move away from said substrate.
 7. The semiconductor device as recited in claim 6 wherein said first layer has a compressive stress value ranging from about 30 MPa to about 40 MPa and said second layer has a compressive stress value ranging from about 70 MPa to about 90 MPa.
 8. The semiconductor device as recited in claim 1 wherein each of said first and second layers has a thickness ranging from about 100 nm to about 300 nm.
 9. A method for manufacturing a semiconductor device, comprising: providing a substrate; and forming a graded capping layer over said substrate, wherein said graded capping layer includes at least two different layers comprising the same material, wherein first and second layers of said at least two different layers have different stress values.
 10. The method as recited in claim 9 wherein providing a substrate includes providing an interlevel dielectric layer.
 11. The method as recited in claim 10 wherein providing an interlevel dielectric layer includes providing an interlevel dielectric layer comprising fluoro-silicate glass.
 12. The method as recited in claim 9 wherein forming a graded capping layer including at least two different layers includes forming a graded capping layer including from about 2 to about 6 different layers, each of said different layers having different stress values.
 13. The method as recited in claim 9 wherein said first and second layers have different compressive stress values.
 14. The method as recited in claim 13 wherein said compressive stress values of said first and second layers increase as said layers move away from said substrate.
 15. The method as recited in claim 14 wherein said first layer has a compressive stress value ranging from about 30 MPa to about 40 MPa and said second layer has a compressive stress value ranging from about 70 MPa to about 90 MPa.
 16. The method as recited in claim 9 wherein forming a graded capping layer includes forming a graded capping layer using a dual frequency RF power ranging from about 500 Watts to about 700 Watts.
 17. The method as recited in claim 9 wherein forming a graded capping layer includes forming a silicon rich oxide graded capping layer.
 18. An integrated circuit, comprising: transistors located over a semiconductor substrate; an interlevel dielectric layer located over said transistors; a graded capping layer located over said interlevel dielectric layer, wherein said graded capping layer includes at least two different layers comprising the same material, wherein first and second layers of said at least two different layers have different stress values; and interconnects located in said interlevel dielectric layer for contacting said transistors and thereby forming an operational integrated circuit.
 19. The integrated circuit as recited in claim 18 wherein said first and second layers have different compressive stress values and further wherein said compressive stress values of said first and second layers increase as said layers move away from said substrate.
 20. The integrated circuit as recited in claim 18 wherein said transistors are selected from the group consisting of: CMOS devices; BiCMOS devices; and bipolar devices. 